Process of producing random three-dimensional crimped acrylic fibers

ABSTRACT

Acrylic homocomponent fiber having random three-dimensional crimp is prepared by stuffer-box crimping tow under hot-wet conditions, cooling the crimped tow and then crimping the tow again under hot-wet conditions. These fibers, in staple form are especially suited for use in preparing improved sliver knit pile fabrics.

'ited States Patent [191 agell 5] Feb. 12, 1974 [54] PROCESS OFPRODUCING RANDOM 2,968,857 1/1961 Swerdloff et al 28/72.l4

THREEDIMENSIONAL CRIMPED 1;; lg/lurfhie et a]. tan ey ACRYLIC FIBERS3,174,208 3/1965 Saito et al.. 28/1.6 X [75] Inventor: Ronald A. Hagell,Lugoff, S.C. 3,259,953 7/1966 Baer 28/1.3 3,399,177 8/1968 Reader161/173 X [731 Asslgneel and 3,447,998 6/1969 Fitzgerald 161/173 p yWflmmgton, 1391- 3,461,521 8/1969 Eskridge 28/7211 [22] Filed: July 15,1971 [21] Appl 1 3 037 Primary Examiner-Louis K. Rimrodt Related US.Application Data [62] Division of Ser. No. 761,160, Sept. 20, 1968, [57]ABSTRACT abandoned.

Acrylic homocomponent fiber having random three- [52] US. Cl. 28/72.11,28/7214 dimensional crimp is prepared by stuffepbox crimping [51] lilt-C] D02g tow under hot wet condiions cooling the crimped Field of. Search1.6, tow and then the tow g i under hot wet 161/173 conditions. Thesefibers, in staple form are especially [56] e ere es Cite Egress-for usein preparing improved sliver knit pile UNITED STATES PATENTS 2,865,08012/1958 Hentschel 28/].3

3 Claims, No Drawings PROCESS OF PRODUCING RANDOM THREE-DIMENSIONALCRIMPED ACRYLIC FIBERS CROSS REFERENCE TO RELATED APPLICATIONS Thisapplication-is a divisional of application Ser. No. 761,160, filed Sept.20, 1968, now abandoned.

The invention relates to a novel process for producing improved acrylicfiber.

BACKGROUND OFYTHE INVENTION In recent years, pile fabrics made by thesliver knit route have become commercially important for producingsimulated furs used in fur coats and other garments, for linears injackets, raincoats, and topcoats, and for other textile articles such asthrow rugs. Acrylic fibers have been used in a large part of this marketbecause of the highly desirable bulk, cover, and softness of thefinished sliver knit pile fabrics.

In the production of the sliver knit fabrics, a sliver of staple fibersis fed to a knitting machine in such a way that tufts of fiber areremoved from the sliver and engaged by the thread being knitted intofabric with the free ends of the fibers in each tuft projecting from oneside of the fabric. The surface of the pile fabric is then sheared tothe desired pile height and subjected to fur ironing (also calledelectrifying) to smooth, parallelize, and polish and fibers comprisingthe surface of the fabric; after which the fabric may again be shearedto trim the surface 'to a uniform height. A large fraction of the weightof the staple fiber starting material is frequently converted to wastein the production of these fabrics, especially in making liner fabrics,since the desired height of the pile is frequently much less than halfof the length of the staple fibers in the sliver. Although it has beenconsidered a desirable goal to make the sliver from staple fibers shortenough to provide approximately the desired pile height and minimizeshearing losses, the conventional acrylic fibers available in the tradehitherto do not cohere sufficiently well in sliver form to permit theproduction of acceptable sliver when the staple fiber length is lessthan about 1% inches, leading to excessive sliver breakage and stacklosses in the knitting step. The starting material sliver is accordinglyformed from staple fibers long enough to provide a sliver strong enoughto be readily processed.

While it is desirable from the viewpoint of sliver cohesion to employacrylic fibers which are well crimped and have sufficient stability toretain their crimp during sliver processing, the production of pilefabrics also requires that the'crimp be removed and the fiber pulled outto a permanently straight condition at the fabric surface in the furironing step. On the other hand, it is desirable to retain as much crimpin the fiber as possible at the base of the pile, so that the fabricwill have a high degree of cover and will not seem thin." Unfortunately,the conventionally crimped acrylic staple fibers available in the tradehave sufficient crimp stability that it is frequently necessary to furiron sliver knit pile fabrics several times to obtain the requireddegree of smoothness, luster, and polish in the surface of the pilefabric. When repeated passages of the pile fabric through the fur ironerare required, the-cost of finishing is greatly increased. The extensiveworking of the fabtie also tends to reduce its cover to a lower levelthan desired.

SUMMARY OF THE INVENTION 2. cooling the crimped tow to less than about60C.,

and 3. reheating with steam to a hot and wet condition,

, and

4. stufi'er box crimping the reheated tow while hot and wet.

The resultant crimped tow preferably is then cut into staple form anddried if necessary. The staple form is especially well suited for use inpreparing sliver knit pile fabrics.

It is to be understood that the term wet is used herein to characterizethe moisture content of the tow, i.e., the wet tow contains a measurablewater content (e.g., greater than about 1 percent by weight) althoughthe tow does not necessarily feel wet to the touch.

In a preferred process embodiment of the invention, (sometimes referredto herein as Process Embodiment A) drawn homocornponent acrylic tow is:

l. crimped at 60 C. while wet (preferably 60 90% water by weight) bypassing the tow through a stufi'er box crimper;

2. cooled below 60C. while maintained wet (preferably 30 50 percentwater by Weight) immediately following crimping; and

3. crimped at 95C. while wet (preferably 30 50 percent water by weight)by passing the tow through a stuffer box crimper.

The fibers are preferably cut into staple length fiber and then dried.

In another preferred process embodiment of the invention (sometimesreferred to herein as Process Embodiment B), drawn homocornponentacrylic tow is:

l. crimped at 60 70Cqwhile wet (preferably 60 percent water by weight)by passing the tow through a stuffer box crimper;

2. cooled below 60C. immediately following crimp- 3. dried while in a'condition free to relax; and

4. crimped at 80 C. while wet (preferably about 2 percent water byweight) by passing the tow through a stuffer box crimper.

The fibers are preferably cut into staple length fibers; no drying isnecessary.

The crimping temperatures are suitably maintained by conventional means.For example, the fibers are preferably heated by steam immediately priorto passing into the stuffer chamber.

The crimping moisture level in the first crimping step is preferablyattained simply as a result of the water content of the tow immediatelyafter it is washed and drawn (e.g., as in a typical continuous processfor producing acrylic fiber). It is important in Process Embodiment Athat the fiber be maintained wet after the first crimping, although thisis not significant if the fibers are to be subsequently dried as inProcess Embodiment B.

The cooling step immediately following crimping is important, otherwisethe crimp may be pulled out in subsequent processing.

The crimping moisture level, in the second crimping step in ProcessEmbodimentA, is attained by maintaining the moisture level in thecooling step which immediately follows the first crimping step. Thecrimping moisture level in the second crimping step in ProcessEmbodiment B is attained preferably by heating the tow in 100C. steamfor less than about one second.

The stable fiber cut from tow produced as above has randomthree-dimensional crimp and forms sliver of excellent cohesion, whichcan be readily converted to a sliver knit pile fabric, even when thestaple fiber length is below an inch (down to about k inch). This highercohesion permits the use of staple lengths shorter than the lower limitof about 1% inches length of conventionally crimped acrylic staple whichcould be used without excessive sliver breakage and stack losses duringknitting. Since a lower minimum staple fiber length is provided by thisinvention, a significant reduction in waste from shearing losses isrealized; the fiber length may be short enough to more closelyapproximate the desired pile height. Furthermore, thesethree-dimensionally crimped fibers also offer significant improvement inthe fur ironing particularly in cover and fabric aesthetics (e.g.,smoothness, luster and polish). For example, sliver knit pile fabricsprepared according to the preferred process referred as ProcessEmbodiment A above, can be fur ironed to a given level of smoothness,luster and polish much more readily than fabrics made from conventionalacrylic fibers, only about half the number of passage through the furironer being required. Surprisingly, better cover is obtained whilerealizing reduced finishing costs. The fabrics prepared by the processreferred to as Process Embodiment B above, for the same number of furironing passages as the conventional fabrics, have excellent smoothness,luster and polish, and strikingly enhanced cover compared thereto.

The fibers of this invention which are more easily fur ironed (e.g.,those prepared by Process Embodiment A above) have unique crimpproperties. In addition to a random three-dimensional crimp whichresults in greater fiber cohesion (as is characteristic of all of thefibers of this invention), the crimp is more readily removed during furironing, i.e., the crimp is not pulled out during knitting, but iseasily ironed out during fur ironing. Due to the ease in fur ironing,the portion of the fiber nearest to the fabric surface is pulledpermanently straight in fewer fur ironing passages and thereforeadditional passages which remove the fiber crimp at the base of the pileare not necessary. Many of the fibers possessing this crimp property arecharacterized by the unique temperature-tension spectra stated above,i.e., when the fiber is placed under a tension of 2 milligrams perdenier at room temperature, it exhibits substantially no increase intension, when heated to a temperature of 135C., compared to significantincreases in tension in conventionally crimped acrylic fibers. Althoughthe invention is not to be limited by the underlying theoreticalconsiderations, it is believed that this unique temperature-tensionspectra explains that the ease of crimp removal in that the repeated furironing passages are generally performed at approximately 135C. (e.g.,121C. (250F.) being quite common) and the crimp is removed with lessforce being necessary to straighten the fiber.

DEFINITIONS The term acrylic fiber," as used herein, refers to a fiberof any long chain synthetic polymer composed of at least percent byweight of acrylonitrile units of the formula,

in the polymer chain.

As is well understood, acrylic fibers may be formed from the homopolymerof acrylonitrile or from copolymers of acrylonitrile andmonoethylenically unsaturated monomers polymerizable with acrylonitrile.Nonlimitative examples of preferred comonomers include methyl acrylate,methyl methacrylate, vinyl acetate, styrene, methacrylonitrile, vinylchloride, vinylidene chloride, methyl vinyl ketone, 2-vinylpyridine, 4-vinylpyridine, 2-methyl-5-vinyl-pyridine, and sodium styrene sulfonate.Preparation of these polymers is well known, such processes beingdisclosed in US. Pat. Nos. 2,486,241; 2,456,238; 2,837,500; and2,837,501 as well as many other patents.

The term homocomponent fiber refers to a fiber spun from a single sourceof polymer feed, so that the cross section of the fiber hassubstantially the same polymer composition at any point excludingparticulate matter which may be present in small quantities as adelusterant dye, etc. or other auxiliary purpose.

The term random three-dimensional crimp" refers to crimps which lie in aplurality of planes randomly along the fiber, as distinct from atwo-dimensional saw-tooth crimp characteristic of conventional singlestuffer box crimping. Such three-dimensional crimp, as shown in FIG. 1,lies randomly in the plane of the photograph as well as in planestransverse thereto.

Measurements and Tests Temperature-Tension Spectra The tension exertedby fibers upon heating is determined by running a tension-temperaturespectrum of a sample of the fibers. The values reported in the examplebelow are determined in accordance with the following procedure.Sufficient filaments, from a sample of a tow from which the staplefibers are cut, are aligned to make a sample of about -200 denier. Thefilaments are cut to a length of 36 cm., handling the filamentscarefully so that they do not become stretched. The filaments aregathered together into a strand and the strand is tied in a loop andweighed. The loop of fiber sample to be tested is placed in an ovenconsisting of the vertical leg of an inductively heated D-shapedaluminum tube having an inside diameter of 0.25 inch and having openingsat the top and bottom of the vertical leg. The top of the loop isfastened in a clamp attached to a transducer (commercially available asa Stratham transducer, operating on the Wheatstone Bridge principle).The bottom of the loop is fastened to another clamp which elongates thefiber strand by means of an adjusting screw to a calibrated tension of 2milligrams per denier, based on the loop denier (twice the denier of thestraight sample from which the loop is formed). The temperature of theoven and the tension measured by the transducer are continuously andautomatically recorded on a chart using conven-. tional, commerciallyavailable instrumentation. The

oven is heated at the rate of 20C. per minute and a curve showing thetension of the fiber with respect to temperature as it is heated iscontinuously recorded. Crimps Per Inch The number of crimps perv inch ina fiber multiply crimped according to this invention, is determined by(l) measuring the length of a single fiber, at least 1% inch long, undera tensioning weight of 150 mg.; and after relaxationof the tension, (2)counting the number of crimps (each crimp defining a complete sine wave)in the fiber when under a lower tension provided by a 5 mg. weight. Thecrimps per inch is calculated by dividing the number of crimps by themeasured fiber length in inches. Crimp Index The crimp index refers tothe change in length of the crimped fiber, at least 1%. inch long, (1)under a tensioning weight of 150 mg.; and (2) after relaxation of thetension, under a weight of 5 mg. The change in length is expressed as apercentage of the uncrimped length.

For staple fibers cut shorter than 1% inch, the crimps per inch andcrimp index are determined on separate samples of longer fiber cut fromthe same supply and processed in the same manner subsequent to cutting.

The invention will be further illustrated by the following example.

EXAMPLE This example illustrates (A) the preparation of crimped fibersaccording to this invention and (B) the use of such fibers in preparingsliver knit pile fabric. The improvement provided by this invention isreadily seen from the comparison of fabrics of fibers of this inventionwith fabrics of the control fibers.

Part A: Crimped Fiber Preparation A multifilamentary tow comprisedessentially of 93.6 percentacrylonitrile, 6 percent methyl acrylate, and0.4 percent sodium styrenesulfonate is simultaneously drawn 4.5X andextracted in a water bath maintained near its boiling point. Afterdrawing, the tow has a tow denier of approximately 320,000 and a denierper filament of about 2.1. The wet tow, containing about 60 90 percentwater by weight is steam heated to a temperature of 68C., is passed at arate of 425 yards per minute between driven feed rolls 2.5 inches wideinto a stuffer box crimper into which steam at a pressure of 20 poundsper square inch is injected. A clapper pressure of 18 pounds per squareinch is applied at the exit of the stuffer box crimper. The wet tow fromthe crimper contains 34 percent water by weight and has a shrinkage of20 percent, when boiled off and dried at a temperature of 110C. for 30minutes. The wet tow is cut to staple fibers having a cut length of 1%inches on a Beria cutter (rotary cutter), dried on a continuous flat-beddryer at 127C. for minutes, and baled. The resulting staple fibers havea regular, two-dimensional, herringbone crimp; this product isdesignated as the Control Sample. The properties of these fibers aregiven in Table I below.

The following preparation illustrates the preferred process of thisinvention previously referred to as Process Embodiment A. Two ends ofthe wet tow, crimped by passing it through the stuffer box .crimper oncein accordance with the above procedure, are combined and passed betweenperforated plates wherein the product is subjected to treatment withsteam at 100C. for contact time of 0.75 seconds. The wet, steamtreatedtow is then passed directly at a rate of yards per minute between drivenfeed rolls 6 inches wide into a stuffer box crimper. A clapper pressureof 15 to 20 pounds per square inch is applied at the exit of thestufferbox crimper. The wet tow from the crimper contains 20 percentwater by weight and has a shrinkage substantially no increase in tensionwhen heated to a temperature of 135C; these characteristics are distinctfrom those exhibited by the Control Sample Fibers. This (Sample A)Process Embodiment A fiber exhibits a minimum tension transitiontemperature which is 10C. higher and a reduced rate of tension rise withincreasing temperature beyond this minimum tension transitiontemperature, when compared to the Control Sample Fiber.

The following preparation illustrates the second preferred process ofthis invention previously referred to as Process Embodiment B. A portionof the wet, oncecrimped tow which is prepared according to the proceduregiven at the beginning of this example is dried by passing it on acontinuous flat-bed dryer at 135C. for 10 minutes. Two ends of the driedtow are combined and the product is passed between perforated plateswherein it is subjected to treatment with steam at C. for a contact timeof 0.75 second. The steamtreated, once-crimped tow, slightly damp fromthe steam pre-treatment, is then passed directly at a rate of 70 yardsper minute between driven feed rolls 6 inches wide into a stuffer boxcrimper. A clapper pressure of 20 pounds per square inch is applied atthe exit of the stuffer box crimper. The tow from the crimper contains2.5 percent water by weight and has a shrinkage of 1.5 percent whenboiled off and dried at C. The substantially dry tow is cut to staplefibers having a cut length of 1 inch on a Beria cutter and baled. Theresulting staple fibers have a random, three-dimensional crimp; thisproduct is designated as Sample B. The properties of these fibers arealso given in the Table I below.

Table I Fiber Properties Control Sample Sample A Sample B Tenacity (gpd)2.3/2.8 2.9/2.2 2.6/ Elongation 26.5/30.5 293/212 20.0] Initial Modulus(gpd) 50.71519 48.2/43.9 46.0/ Crimps Per Inch l0.0/10.9 12.1/12.512.3]! 1.0 Crimp Index 12.2/16 6.0/8.7

Part B: Sliver Knit Pile Fabric 19 courses per inch and 12.5 wales persquare inch. Three control sample fibers at 1% inches staple length areabout the shortest conventionally crimped staple length that issuitable; shorter lengths are not sufficiently cohesive which results insliver breakage during knitting. Significantly, the fibers of thisinvention, at this one inch staple length (and even at shorter lengths)are sufficiently cohesive during knitting.

Each of the sliver knit fabrics are sheared (on a pile shear machinemade by the Parks and Woolson Co.) to a pile height of three-eightsinch.

The sheared fabrics are then subjected to fur ironing to smooth,parallelize and polish the fibers (on a fur ironing machine made byFrank Egan and Co.). The fabrics are each ironed at a rate of 6yds./min. in each of 4 passages through the fur ironer. The temperaturefor the first passage in 400F. (232C.) and 250F. (121C.) for each of thenext 3 passages. Portions of each of the three fabric samples areremoved after each passage through the fur ironer. The final (i.e.,after the fourth passages) fabrics are again sheared to a pile height ofthree-eights inch as above.

The portions of the three fabrics after each fur ironing stage areexamined for cover, smoothness, luster and polish. Quite surprisingly,the Process Embodiment A fabric has better cover, smoothness, luster andpolish after two fur ironing passages, than the control fabric has afterfour such passages. The process Embodiment B fabric, after the samenumber of fur ironing passages as the control fabric, has excellentsmoothness, luster and polish, and strikingly enhanced cover compared tothe control fabric. Thus, using either of these two process embodimentsof this invention, an improvement over conventionally crimped acrylicfibers is realized.

What is claimed is: 1. Process for producing fibers of randomthreedimensional crimp comprising:

1. stuffer box crimping homocomponent acrylic tow while hot and wet;

2. immediately cooling the crimped tow to less than about 60C.;

3. reheating the cooled crimped tow with steam to a hot and wetcondition, and

4. stuffer box crimping the reheated tow while hot and wet.

2. Process of claim 1 wherein:

said tow in said crimping step (1) is maintained at a temperaturebetween about 60 to C.;

said cooling step (2) immediately follows said crimping step (1) andmaintains the said crimped tow in a wet condition; and

said crimped tow in said steps (3) and (4) is maintained at atemperature of between about to C. by contacting it with steam prior toentering the stuffer box.

3. Process of claim 1 wherein:

said tow in said crimping step (I) is maintained at a temperaturebetween about 60 to 70C.;

said cooling step (2) immediately follows said crimping step (I); and

said crimped tow in said steps (3) and (4) is maintained at atemperature between about 80 to 95C. by contacting it with steam priorto entering the stuffer box;

said process further comprising the step of drying the crimped tow, in acondition free to relax, after cooling step (2), but prior to step (3).

2. immediately cooling the crimped tow to less than about 60*C.; 2.Process of claim 1 wherein: said tow in said crimping step (1) ismaintained at a temperature between about 60* to 70*C.; said coolingstep (2) immediately follows said crimping step (1) and maintains thesaid crimped tow in a wet condition; and said crimped tow in said steps(3) and (4) is maintained at a temperature of between about 80* to 95*C.by contacting it with steam prior to entering the stuffer box. 3.Process of claim 1 wherein: said tow in said crimping step (1) ismaintained at a temperature between about 60* to 70*C.; said coolingstep (2) immediately follows said crimping step (1); and said crimpedtow in said steps (3) and (4) is maintained at a temperature betweenabout 80* to 95*C. by contacting it with steam prior to entering thestuffer box; said process further comprising the step of drying thecrimped tow, in a condition free to relax, after cooling step (2), butprior to step (3).
 3. reheating the cooled crimped tow with steam to ahot and wet condition, and
 4. stuffer box crimping the reheated towwhile hot and wet.